Protective relaying with discriminative reclosure



Sept. 7, 1943. s. GOLDSBOROUGH ETAL 2,329,043

PROTECTIVE RELAYING WITH DISCRIMINATIVE RECLOSURE Filed Dec. 30 1941 2 Sheets-Sheet 2 cac 75220527712 far ATTORNEY Patented Sept. 7, 1943 UNITED STATES PATENT OFFICE PROTECTIVE RELAYING WITH DISCRIBIINATIVE RECLOSURE Shirley L. Goldsborough, Basking Ridge, N. 1., and Boy M. Smith, Fairfield, Conn, assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December so, 1941, Serial No. 424,953

11 Claims. (01. 175-294) 1 low-voltage systems (as transmission-voltages go), a liveIphase-wire lying on the ground, or against a tree or other object, presents a distinct hazard to life, but if the ground is hard and dry it may not draw sufllcient current to actuate even the most sensitive residual-current or groundfault relays for a matter of several minutes, or even hours, particularly after the phase-wire is lying quietly on the ground or other object, without moving. Such a condition obviously represents a life-hazard which cannot be ignored. If,

however, the transmission line is faulted by rea- -A more specific object of our invention is to apply the discriminatory-reclosure idea just described to a single-pole tripping-scheme in which service-continuity is enhanced, in the event of a fault involving only a. single line-conductor, by tripping out only that one line-conductor, by means of a single-pole circuit-breaker at each end of the protected-line section, and immediately reclosingthe tripped single-pole breakers; but, in

accordance with our invention, means are provided for preventing :such vreclosure in case the fault involved insuflicient line-current to indicate thepresence of a grounding arc.

With the foregoing and other objects in view,

our invention consists in the circuits, combinations, apparatus, parts, methods and systems hereinafterdescribed and claimed, and illustrated .in the accompanying drawings, wherein Figure 1 is a schematic view of circuits and apparatus embodying our invention in a simplified carrier-current relaying system,

Fig. 2 is an across-the-line diagram of the protective relaying system shown in Fig. 1, and I 'Fig. 3 is an across-the line diagram of a P tective relaying system for utilizing single-pole tripping and ,reclosure.

In Fig. 1,'we have shown'our invention as being embodied as a part of a simplified or inexpensive carrier-current relaying-system for the protection of a three-phase line 4 which is fed from a. bus 5 which maybe fed from a delta-star step-up power-transformer ,6. It will be understood that similar protective equipment is provided atboth ends of the protected line-section 4, but as the equipments at the two ends-are similar, an illustration and description of one will sullice for both.

In the system shown in Fig. 1, the line 4 is protected by a three-phase circuit-breaker CB, which is provided with a trip-coil TC, 9. closingcoil CC, and three auxiliary switches or backcontacts "I, 8, 9, which are-closed when the circuitbreaker is closed, and which open when the circuit-breakeropens.

The relaying system shown in Fig. 1 is a carrier-current system, involving a carrier-current transmitter, which is symbolized by a triode oscillator-valve H, a carrier-current receiver, which is symbolized by a triode receiver-valve l2, and a polarized receiver-relay RR, having a restraining or holding-coilRRH-which is energized from the anode-circuit I30! the receiver, and, an operating or tripping-coil RRT which is controlled by the protective relays.

The protective relays, in the simplified carriercurrent system shown inFigs. 1 and 2, comprise a polyphase directional relay D, having volta coils M which are energized from potentialtransformers l5 connected to the bus 5, and current-coils 16 which are energized from the respective phase-currents of the line, as delivered by a bank of star-connected line-current transformers ll (Fig. 1). We also use a residual-current or ground-directional relay D0, which has aresidual-current coil 18 which is connected in the neutral circuit of the current-transformers ,H, and a polarizing-coil l9 which is shown as deriving its energization from an auxiliary current- .transformer 2| in thegrounded neutral circuit of tive overcurrent relays 1A3, B3, 103 and 108.

will be referred to in the description of the operation, which is as follows:

The transmitters-oscillator II is normally in a non-transmitting condition by reason of the fact that its grid-circuit 22 is connected to the negative bus, while its cathode-circuit 23 is at or near I the potential of the positive bus, being connected thereto through a resistor 24.

When a fault involving ground-current," or residual current, occurs on the protected line section, the ground-fault relays IO and I03 respond to the residual current, and the grounddirectional relay DO responds to an into-the-linelooking direction of the residual current' The sensitive ground-relay I03 instantly initiates carrier-transmission by connecting the oscillatorcathode 23 to the negative bus, through a circuit which includes the back contacts of an auxiliary relay SP which will be subsequently referred to more in detail. The ground-directional relay DO, and the groundovercurrent relay IO energize a partial tripping-circuit from the negative bus, through a small resistance 25, to a conductor 26 which will be referred to after some consideration has been given to phase-fault tripping.

In the event of a line-fault involving a material line-current inone or more of the phaseconductors of the three-phase line l, carriercurrent transmission is started by the contacts of one or more of the sensitive phase-'overcurrent relays 1A3, IB3 or 1C3, which connect the oscillator-cathode 23 to the negative bus. At the same time, the phase-directional relay D responds to an into-the-line-looking direction of the polyphase line-current; and one or more of the phase-overcurrent relays IA, IE or IC respond to the line-current; thus again establishing a circuit from the negative bus to the rent response IO) energy is supplied to the coil of anauxiliary relay -SP, the circuit of which is completed through a resistor 28, and thence to the positive bus. This SP relay thus responds to an internal, or into-the-line-looking, direction; and when the fault-current has-this intothe-line-looking direction at both ends of the protected line-section, carrier-current is removed irom both ends-of said line-section, by the opening of the SP back-contacts in the cathode energizing-circuits of the carrier-current transmitters. When carrier is removed from both ends of the line-section, thereceiver-relayholding-coil RRI-I, which is connected in the anodecircuit 13 of the receiver-tube 12, is deenergized.

The responseof the SP relay has also another tioned conductor 26, through the RR make-contact, the trip-coil TC, and the auxiliary breakerswitch 9.

In accordance with our invention, we utilize means for effecting a discriminatory reclosing of K the circuit-breaker CB when it is tripped, re-

effect, because its back-contact SP is in shunt 4 which may be traced from the previously mento the positive bus. stantly energizes theclosing-coil CC-of the circlosing only for those ground-faults which draw enough current to indicate the possibility of an arcing fault, and not reclosing for those groundfaults which might involve a broken live lineconductor lying on dry ground. In the system I,

as shown in Figs l and 2, we utilize, for this purpose, the auxiliary relay K, which is energized whenever a tripping circuit is completed, to the conductor 23, through the phasedirectional contacts D, the phase-overcurrent contacts IA, IBxor IC, and the conductor 21. However, it will be noted that the auxiliary-relay coil K is not energized when a tripping circuit is completed, to the conductor 26,. through the ground-fault-responsive circuits, vincluding the contacts of the sensitive ground-directional relay DO and the residual-current relay IO, which is much more. sensitive than the phase-fault relays IA, IB and IC. Ihus one of the phase-fault relays IA, IE or IC, responds whenever a groundiault on itsparticular phase draws a material amount of line-current, sufficient to indicate the possibility or probability'of' an arc, while the residual-current ground-directional and roundfauit relays DO and I0 are necessarily made as sensitive as possible, soas to respond even when a line-conductor is lying on a hard, dry ground of very high resistance, which does not form an arc. The small resistance 25 is included inthe groundfault tripping-circuit to the conductor. 26, for the purpose of preventing the short-circuiting of the coil K when this ground-fault tripping? circuit is energized. The resistance 25, should be very small, something like the. order of mag nitude of the resistance of the coil K, moreor less (the coil K being an overcurrent coil of very lowjresistance), so that. no material amount of impedance is imposed-inthepath of. the relatively heavy tripping-current which is momentarily passed through the trip-coil TC.

When the auxiliary relay. K selectively responds to a tripping-operation which is accompanied by an internal direction of a line-current 0f iault-magnitude, it is utilized to eiiect the reclosure oi the, circuit breaker, by any suitable means. In the particular embodiment of our invention which is shownin Figs. 1 and 2, the closure of the make-contact K energizes the coil of a closing-relay X, through a circuit which can be traced from the negative bus, through the contact .K, the back-contact 39 of. a tripping push-button PB, the back-contact of a toggle or latched relay R, a conductor 35, the X-coil, and the back-contact'of a cutofi-relay Y, and thence The. closing-relay X incuit-breaker, through two of the make-contacts 32 and 33 of the closingerelay X. At the same time, the closing-relay X seals itself in, through its thirdrnake-contact 3:2, which shunts the circuit consisting of the K-contact, the push-button back-contact 39, and the R-relay back-contact. The coil of the cutoff-relay Y is energized through a circuit which can be traced from the conductor 3|, thev .Y-coil, and. the auxiliary breaker-switch 3, to the'positive bus. The cutoff-relay Y preferably, although not necessarily, has a slow pickup of two or three cycles, more or less, which-is symbolically indicatedby means of a dashpot 35 which permits the relay to drop out substantially instantaneously. The pickup delay, when utilized, is for the purpose of pen mitting the breaker-switch 8 to get open, during the opening stroke of the circuit-breaker, before the cutoff-relay back-contact Y is opened. In this way, we avoid a momentary opening and closing of the reclosing-rela'yX at the very beginning of the opening stroke of the circuitbreaker.

At the same time that the closing-coil CC is-energized, the coil of the toggle or latched relay R is also energized, from the make-contact 32 of the closing relay X. The toggle or latched relay R is a relay of the type which will stay in'whatever position it is moved to, even after the deenergization of the coil which caused it to move to that position, and this relay will keep its position until something positive is done to the relay to change its position. A toggle relay is commonly used, but for illustrative purposes, we show the relay R as being of a latched type, as shown in Fig. 1, having a latch 36 which holds the relay in its actuated position, when it is picked up as a result of an energization of its operating-coil R. The latch 36 is released by means of a latch-coil L. The toggle or latched relay R. is provided with a back-contact which ,has already been referred to in the description of the energizing'circuit for the closing relay X, and a make-contact which is utilized to energize a timer-coil T from a 115-voltalternating-current circuit, through the breaker-switch I, so that the timer T will begin to move when the breaker finishes its reclosing-stroke. The timercontact T is utilized to energize the unlatchingcoil L.

It will be noted, from the foregoing, that the closing-coil CC of the circuit-breaker is ener-' glzed practically as soon as the tripping-coil TC is energized, the only delay being the negligible delays due to the necessary operating-times of the instantaneously operating relays K'and X.

The time-constant of the closing-coil CC is so 45 large, however, that the circuit-breaker has time to open its main contacts far enough to interrupt the arc, before the circuit-breaker mechanism starts to reclose. In an illustrative example, the circuit-breaker requires some twenty-five cycles to reclose itself after the initial trippingin'ipulse, assuming a -cycle line, although our invention is not limited, of course, to any particular closing-time.

The closing-coil CC is deenergized by the reclosure of the circuit-breaker, which closes the auxiliary breaker-switch 8, energizing the cutoffrelay Y through a circuit which can be traced 7 from the positive bus, through the breakerswitch 8, the cutoff Y-coil, and the X-contact 34, to the negative bus. When the cutoff-relay Y is energized, it picks up, either instantly, or in a very few cycles as determined by the dashpot 35 (if used), opening its back-contact Y and deenergizing the closing-relay X and hence the closing-coil CC.

When the circuit-breaker recloses, if the fault still exists on the line, the trip-coil circuit will again instantly be energized, again tripping the breaker, but it will be noted that the closingcoil circuit will not again be energized because of the now-open back-contact of the toggle or latched relay R in the circuit of the X-coll. While we have thus provided for only one reclosure of the circuit-breaker, it is well understood, in the recloslng circuit-breaker art, that a cycle-counter may be utilized to provide for as many reclosures as may be desired, before the circuit-breaker is finally tripped out, and we desire our illustration to be construed as being typical of any desired type of reclosure-means. The timer T is set for any convenient time, which may be of the order of from five to twenty seconds, depending upon the particular operating-conditlons, and designed to provide a timedelay long enough to make sure that the arc which constituted the fault, in the first place, is not going to restrike itself again. If the circuit breaker remains reclosed, without reopening for thetime for which this timer T is set, the timercontacts T are closed, thus energizing the latchcoil L and restoring tht toggle or latched relay Rto its initial or unresponsive position, ready for a new cycle of operations as hereinabove described.

- In Fig. 3, we have shown our invention applied to a single-pole relaying-system such as that which is covered by an S. L. Goldsborough application, Serial No. 424,957, filed December 30,

1941. In this single-pole switching-system, three single-pole circuit-breakers, designated CBA, C33 and CBC, are connected in the respective phase-conductors of the protected three-phase line-section at each end thereof, these circuitbreakers having trip-coils TCA, T03 and TCC, and closing coils CCA, CCB and COO. This sin gle-pole system is designed to distinguish between 8 single line to-gr'ourid fault, which affects only one of the line-conductors, and phase-faults affecting two or more of the conductors; and if only one line-conductor ls faulted, only they single-pole breakers at the two ends of that particular line-conductor are opened, and immediately reclosed again, meanwhile transmitting single-phase power over the two unfaulted lineconductors during the 25-cy'cles, (more or less) necessary to trip out, and reclose, the singlepole breaker at each end of the line-section. If the single-ground fault still persists on the line after such reclosure, all of the single-pole breakers are tripped out; or if a fault should occur, involving two or more phases, all of the singlepole breakers are tripped out in the first place, without any reclosing.

In accordance with our invention, means are provided for discriminating between those single-ground faults which draw enough current to indicate the presence'of an arc, and those which do not; reclosing the single-pole breaker, at the respective ends of the line-section, only in the eventthat the single-ground fault had a sufflciently low resistance, or a sufiiciently high conductance, to indicate the possibility of an arc.

Referring, in detail, to the single-pole switching-system shown in Fig. 3, it will be noted that we have provided separate tripping-circuits for ground-faults and for phase-faults; and that we have also provided separate tripping-circuits for each of the three single-pole circuit-breakers in the respective phases of the three-phase line.

.The carrier-current control is indicated at the addition to the SP back-contact in the RRT shunting-circuit, we utilize, in Fig. 3, a serially connected back-contact of a phase-fault contactor MK, and also a serially connected back-contact of a ground-fault directionally responsive auxiliary relay SG, with the groundfault carrier-starting contact I03 connected between the MK and SG contacts, so as to be in series with'only the SG contact in the cathodeenergizing circuit 23 of the carrier-current transmitter.

- The auxiliary ground-directional relay SC is energized whenever there is a response of the ground-overcurrent and the ground-directional relays IO and DO, as will be seen from the circuit near the top of Fig.3.

The receiver-relay RR, in Fig. 3, is provided with two make-contacts 40 and 41, one in the ground-fault tripping-circuits, and the other in the phase-fault tripping-circuits.

Whenever there is a ground-fault accompanied by an into-the-line-looking direction at both ends of the protected section, a common conductor 42, for all phases of the ground-fault tripping-circuits, is partially energized, or connected to the negative bus, in a circuit which can be traced, at the top of Fig. 3, from the negative bus, through the coil ofa contactor-switch CS, the make-contacts IO and DO, and the makecontact 43 of the receiver-relay RR, and thence to the aforesaid conductor 42. From the common conductor 42, the ground-fault trippingcircuit branches into three circuits, under the selective control of three ground-fault selectorrelays or contacts, SA, SB and SC, which are designed to selectively designate the faulted phase-conductor of the line, but without reliable discrimination between faults involving only one phase, and faults involving a plurality of phases, or even between fault-conditions and some normal power-conditions.

Assuming, for example, that there is a groundfault involving only the phase-conductor A of the protected line-section and occurring within the limits of the protected line-section, the trip-= ping-circuit is continued, from the common conductor 42, through the back-contact of an auxiliary relay X3, the SA make-contact, the coilof a contactor KA, the trip-coil TCA, and the makecontact or auxiliary breaker-switch CBA of the single-pole breaker in said phase-conductor A. As soon as this trip-circuit is completed, the general ground-fault ccntactor CS, and the phase- A ground-fault contactor KA, are energized. The CS-contactor closes its contact and energizes the XS-coil, thereby blocking ground-fault tripping in the other two phases while the faulted phase, A, is being cleared, and for very few cycles thereafter, this time-delay of a few cycles being secured by means of a slow dropout of .the X3- relay, as obtained by means of a short-circuited coil 43 which is associated therewith.

The phase-A ground-fault contactor 'KA has two make-contacts, 2. KA make-contact 44 which seals-in the KA contactor around the five contacts IO, DO, RR, X3 and SA, and a second faulttrip-circuit response, and which partially sets up a reclosing circuit for the tripped circuitbreaker.

In accordance with our invention, the reclosing KA make-contact 45 which responds substantiaily simultaneously with the phase-A groundcontact, thence to the positive bus.

fault which caused the tripping. By way of illustration, the particular means Which is shown, in Fig. 3, for providing this current-magnitude supervision of the reclosing-means is the makecontact of a second-zone impedance-relay ZZA, it being understood that similar relay-contacts are provided for the other two phases, as indicated at ZZB and ZZC in Fig. 3.

Assuming a response of both the phase-A ground-fault tripping-contactor KA, and the phase-fault relay Z2A for the phase-A line-con ductor, a reclosing circuit is completed through a back-contact of the previously mentioned MK- relay, the back-contact of a phase-A toggle or latched relay RA (corresponding to the relay R in Figs. 1 and 2), the conductor iii, the coil of the phase-A closing-relay XA, and the YA back- From this point on, the closing-operation is similar to that which has already been described for Figs. 1 and 2, it being understood that a separate reclosing-apparatus is provided for each of the three phases A, B and C, as distinguished by the letters A, B and C added to the respective relaydesignations.

If the single line-to-ground fault should persist, or restrike, on the faulted line-conductor (the phase-A conductor has been assumed), immediate retripping is obtained, but a second reclosure is blocked, for the time for which the timers TA, TB and TC are set, by the RA back' contact, corresponding to the R-relay in Figs. 1 and 2.

Since it is undesirable to leave two of the line-conductors carrying power for an extended period of time, after one of the three line-conductors has been finally switched out and locked out of service, we have indicated means for efiecting an opening of thetwo closed circuit-breakers CBB and CBC when the tripped circuit-breaker CBA remains out for a predetermined time during which the other two breakers are not tripped.

In Fig. 3, we have illustrated this function as being accomplished by a master-switch MS, the coil of which is energized through a circuit which is shown immediately underneath the reclosing circuits of the phase-C breaker. If any one of the three single-pole breakers remains open at the time when the toggle or latched relay, RA for example, is reset after a singlepole reclosure-operation, that fact is determined by a circuit-breaker back-contact 41 of the circuit-breaker, for example, CBA, in series with an auxiliary back-contact 48 for the RA relay, thus completing a partial-circuit from the negative bus to the conductor 49. The conductor 49 is joined to one of the terminals 51 of the MS- coil through three parallel-connected circuitbreaker make-contacts 52 of the three circuitbreakers CBA, CBB and CBC, respectively. The circuit-breaker make-contacts 52 are closed whenever the associated breaker is closed.

The circuit-breaker back-contacts 4'! are closed only when the associated breaker is open, but, in general, the RA back-contact 48 will become latched open before the CBA circuit-breaker back-contact 4'! opens during the tripping operation of the breaker. If desired, the MS relay may be given a slightly sluggish pickup, by means which are conventionally illustrated by a, dashpot 53 which is shown associated With each of the three MS make-contacts, in Fig. 3, so as to guard against the possible contingency of a closing of the CBA back-contact 47 an instant before the opening of the RA back-contact.

It the single-phase line-fault is one which clears itself, the tripped single-pole breaker, CBA, will reclose and remain reclosed, so that its backcontact in will be open by the time that the toggle or latched relay RA is reset, and-the masterswitch MS will not be energized. If, however, the tripped circuit-breaker contact CBA has reopened by the time that the RA relay resets, and if, at the same time, either one or the other two circuit-breakers is closed, an energizing circuit will be made to the MS coil, picking up all three of the MS back-contacts, and energizing a direct tripping-circuit from the negative bus, through the respective MS contacts, to the respective tripping-circuits for all three trip-coils 1 7:

TCA, T03 and T00, thusenergizing those trip- .ping coils whose breaker-switches 9 are closed, that is, only those tripping-coils whose breakers are closed.

The reclosing-circuit interlock which is provided by the MK back-contact, in the energizingcircuit of the XA relay just traced, is utilized for the purpose of preventing reclosure of the singlepole breaker in the event that a phase-fault tripping-circuit is completed for one of the phases in which the phase-selector SA, SB or SC, as the case may be, does not respond, thus indicating, by the non-response of the selectorrelay, that there is no single-phase ground-fault on that phase. The phase fault tripping-circuits Will now be described.

The phase-fault tripping-circuit has a common branch which extends from the negative bus, through the coil of the common phase-fault contactor MK, and thence to a common conductor ,1.

54, which is common to all three branches of the phase-fault tripping-circuits. From the common conductor 54, the phase-fault tripping-circuits branch, extending through any one of four parallel paths to a second common phase-fault trip-circuit conductor 55, the four paths including the parallel-connected make-contacts of three second-zone timers TZA, T23 and T20 for the respective phases, and the receiver-relay make-contact ll. 55, the phase-fault tripping-circuits become individualized. As they are all alike, a description of one will suilice for all.

For the phase-A breaker, the tripping-circuit is continued, from the conductor 55, through the make-contact of the second-zone impedance-element ZZA, the make-contact of a phase-A directional relay DA, and the SA back-contact, and

thence to the trip-coil TCA. As soon as a phasefault tripping circuit is energized, for any one of 4 the three phases, in the manner just indicated,

the phase-fault contactor MK will respond, closing its three make-contacts MK which by-pass the four contacts T2, Z2, D and S for each of the phases, thus completing, and holding, a trippingcircuit to each of the three trip-coils TCA, T013 and TCC, resulting in a three-pole tripping-operation. At the same time, the phase-fault contactor MK opens its four back contacts MK. One

of these four MK back-contacts is in series with the SP back-contact in the carrier-control circuit as previously mentioned, while the other three MK back-contacts are in the three reclosure-circuits for the three circuit-breakers, as also previously described.

Th auxiliary phase-directional relay SP, in the form of our invention shown in Fig. 3, is connected between the negative bus and the common phase-fault conductor 55, so that it is energized whenever there is a second-zone phase-fault in- From the common conductor companied by a non-response of the phase-se lector (SA, SB or SC) for the same conductor, this SP-response being obtained before the response of the receiver-relay RR, and, in fact, being the means which is utilized for removing carrier, at each end where the SP-response is obtained, and thus bringing about the response of the receiver-relay RR whenever the SP directional response is obtained at both ends of the protected line-section, as will be understood from the explanation of the carrier-current control which has been given in connection with Figs. 1 and 2.

While we have illustrated our invention in two dilierent forms of embodiment, one being a simplified carrier-current system, and the other being a somewhat more comprehensive single-pole carrier-current system, it will be understood that our invention is not limited to use with carrier, and that it is also not limited to any particular precise form of embodiment; as many changes, in the way of refinements, additions, omissions, and substitutions, may be made by those skilled in the art without departing from the essential principles of our invention. We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their wording.

We claim as our invention:

1. Fault-responsive protective relaying means for controlling the opening-means and the closing-means of a circuit-interrupter in a line to be protected, comprising the combination, with said circuit-internipter, of relaying-means directionally responsive to either a heavy-current or a light-current fault on the protected line for effecting the energization of the circuit-interrupter opening-means, and simultaneously responsive relaying-means, selectively responsive only to a fault-current of sufiicient intensity to indicate the possibility of an arcing fault, for eiiecting the energization of the circuit-interrupter cl0singmeans.

2. Fault-responsive protective relaying means for controlling the opening-means and the closing-means of a circuit-interrupter in a line to be protected, comprising the combination, with said circuit-interrupter, of relaying-means re sponsive to either a line-to-line fault or a groundfault on the protected line for effecting the energization oi the circuit-interrupter openingmeans,'and simultaneously responsive relayingmean, selectively responsive only to an operation resulting in such opening-means energization, and only when accompanied by a fault-current of suflicient intensity to indicate the possibility of an arcing fault, for effecting the energization of the circuitinterrupter closing-means.

3. Fault-responsive protective relaying means for controlling the opening-means and the closing-means of a circuit-interrupter means at both ends of a protected line-section, comprising the combination, with said circuit-interrupter means, of relaying-means directionally responsive to either a heavy-current or a light-current fault on the protected line, and responsive to an intothe-line-looking direction at both ends of the protected line-section, for efiecting the energization of the circuit-interrupter opening-means, and simultaneously responsive relaying-means, selectively responsive only to a fault-current of sufficient intensity to indicate the possibility of at both ends of the protected line-section, for

effecting the energization of only the openingmeans of the circuit-interrupter means.

5. Fault-responsive protective relaying means for controlling the opening-means and the closing-means of a circuit-interrupter in a line to be protected, comprising the combination, with said circuit-interrupter, of relaying-means responsive to either a line-to-line fault or a ground-fault on the protected line for effecting the energization of the circuit-interrupter opening-means, and simultaneously responsive relaying-means, selectively responsive only to a ground-fault, and only when accompanied by a fault-current of sufficient intensity to indicate the possibility of an arcing fault, for effecting the energization of the circuit-interrupter closing-means.

6. Fault-responsive protective relaying means for controlling the opening-means and the closing-means of a circuit-interrupter means at both ends of a protected line-section, comprising the combination, with said circuit-interrupter means, of sensitive residual-current relaying-means, responsive to an into-the-line-looking direction at both ends of the protected line-section, for effecting the energization of the circuit-interrupter opening-means, and simultaneously responsive relaying-means, selectively responsive only to a ground-fault, and only when accompanied by a fault-current of sufficient intensity to indicate the possibility of an arcing fault, for effecting the energization of the circuit-interrupter closing-means.

'7. Fault-responsive protective relaying means for controlling the opening-means and the closing-means of a circuit-interrupter means at both ends of a protected line-section, comprising the combination, with said circuit-interrupter means, of sensitive residual-current relaying-means, responsive to an into-the-line looking direction at both ends of the protected line-section, for effecting the energization of the circuit-interrupter opening-means, line-current relaying-means, responsive to an into-the-line-looking direction at both ends of the protected line-section, for effecting the energization of the circuit-interrupter opening-means, and simultaneously responsive relaying-means, selectively responsive only to a ground-fault, and only when accompanied by a fault-current of sufficient intensity to indicate the possibility'of'an arcing fault, for efiecting the energization of the circuit-interrupter closlog-means.

8. Fault-responsive protective relaying means for controlling the respective opening-means and closing-means of a plurality of single-pole circuit-interrupters in the phase-conductors of a polyphase line-section at both ends thereof, comprising the combination, with said circuit-interrupters, of selective relaying-means for determining which of the line-conductors is faulted, in the event of a single line-to-ground fault within the protected line-section, circuit-means responsive to said selective relaying-means for sub stantially simultaneously energizing the openingmeans of only the single-pole circuit-interrupters at the tWo ends of the particular line-conductor which is faulted, and circuit-means, responsive to such a selective single-pole operation, but selectively responsive only to a fault-current of sufiicient intensity to indicate the possibility of an arcing fault, for efiecting the energization of the closing-means of the affected circuit-interrupters.

9. The combination, with the apparatus recited in claim 8, of means responsive to an open conditicn of any one or more of the plurality of single-pole circuit-interrupters at an end of the protected line-section, accompanied by a closed condition of any one or more of the other singlepole circuit-interrupters at that end, enduring after a tripping-and-reclosure operation, for effecting an opening of the closed circuit-interrupters.

10. Fault-responsive protective relaying means for controlling each of a plurality of single-pole circuit-interrupters in the several phaseconductors of a polyphase line, comprising the combination, with said circuit-interrupters, of selective ground-fault relaying-means for determining which of the line-conductors is faulted, in the event of a single line-to-ground fault on the line, and for causing an opening-operation of only the single-pole circuit-interrupter in that line-conductor, and for automatically thereafter causing a single-pole closing-operation of the same circuit-interrupter, and means for causing said single-pole closing-operation to be selectively responsive only to those single-phase groundfaults that involve at least a predeterminedly high fault-severity in the faulted line-conductor.

11. Fault-responsive protective relaying means for controlling each of a plurality of single-pole circuit-interrupters in the several phase-conductors of a polyph'ase line, comprising the combination, with said circuit-interrupters, of selective ground-fault relaying-means for determining which of the line-conductors is faulted, in the event of a single line-to-ground fault on the line, and for causing an opening-operation of only the single-pole circuit-interrupter in that line-conductor, and for automatically thereafter causing a single-pole closing-operation of the same circuit-interrupter, means for causing said singlepole closing-operation to be selectively responsive only to those single-phase ground-faults that involve at least a predeterminedly high faultseverity in the faulted line-conductor, and phasefault relaying-means responsive only to predetermined fault-conditions involving two or more of the line-conductors for causing opening-operations of one or more of the single-pole circuit-interrupters.

SHIRLEY L. GOLDSBOROUGH. ROY M. SMITH. 

